1. Field of the Invention
The present invention relates to the integration of an electronic circuit. More particularly, the present invention relates to a multichip module comprising a plurality of wafer chips.
2. Description of the Prior Art
Circuit integration of electronic equipment not only provides the possibility of miniaturizing the size of entire electronic apparatuses, but it also offers numerous advantages including improvement in the reliability and reduction of the power consumption of electronic equipment. Accordingly, circuit integration of digital circuits which perform logical operations of binary numbers as well as circuit integration of various types of analog circuits has been attempted.
An integrated circuit which integrates only digital circuits is called a digital integrated circuit. On the other hand, an integrated circuit which integrates only analog circuits is called an analog integrated circuit.
Furthermore, in such digital and analog integrated circuits, an integrated circuit which is integrated on a single wafer chip is called a monolithic integrated circuit.
Monolithic integrated circuits not only provide the possibility of drastically miniaturizing electronic circuits, but also allow improvement of reliability, reduction of power consumption, and the like.
Also, an integrated circuit which integrates a mixture of more than one digital or analog integrated circuit (wafer chip) and, as required, other devices or parts, is called a hybrid integrated circuit.
Compared with monolithic integrated circuits, hybrid integrated circuits allow efficient development of circuit integration of large-scale electronic circuits in a relatively short period of time. Furthermore, hybrid integrated circuits also provide an easy way to realize integrated circuits which use a combination of different processes, such as the accommodation of bipolar analog integrated circuits and CMOS (complementary metal-oxide-semiconductor) digital integrated circuits in the same package.
However, problems such as the relative difficulty of development of integrated circuits of the desired electronic circuits, a longer period of development and higher development costs have been associated with the above-described monolithic integrated circuits.
These problems become especially significant as the scale of the electronic circuits, which are to be integrated, increase.
Furthermore, the difficulty in realizing a change in the design (change in the circuit) is another problem with the above-described monolithic integrated circuits. The need for a major design change involves the problem that the costs and the period of time required for the design change are equal to the costs and time needed for an entirely new development. Development costs for an ordinary monolithic integrated circuit are said to amount to approximately 5 million yen.
In addition, higher process costs are a problem with monolithic integrated circuits when integrated circuits such as BiCMOS integrated circuits are fabricated by employing a different process.
Major circuit elements which are integrated into a single wafer chip are transistors, diodes and resistors. As these circuit elements are limited to those with relatively small capacities, electronic circuits which allow integration into monolithic integrated circuits are subject to numerous restrictions.
On the other hand, a problem concerning the above-described hybrid integrated circuits is a decline in reliability with regard to the conductive tracks which interconnect a plurality of wafer chips, namely, the digital or analog integrated circuits which compose the hybrid integrated circuit.
Another problem is that, due to the interconnecting conductive tracks between a plurality of wafer chips and the like, the mounting area increases, which in turn results in a decrease in the overall degree of integration.
Another issue is the difficulty of handling during production.
Compared with monolithic integrated circuits, the development of hybrid integrated circuits is easy. However, as with monolithic integrated circuits, a change in the design of hybrid integrated circuits is difficult. The need for a major change in the design of a hybrid integrated circuit involves the problem that a long period of time for the design change and high development costs are required. In general, the development costs for a hybrid integrated circuit are said to amount to approximately 1 million yen.